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Cave Dripwater Isotopic Signals Related International Journal of Speleology 48 (1) 63-74 Tampa, FL (USA) January 2019 Available online at scholarcommons.usf.edu/ijs International Journal of Speleology Off icial Journal of Union Internationale de Spéléologie Cave dripwater isotopic signals related to the altitudinal gradient of Mount-Lebanon: implication for speleothem studies Carole Nehme1,2,3*, Sophie Verheyden2,4, Fadi H. Nader5, Jocelyne Adjizian-Gerard6, Dominique Genty7, Kevin De Bondt2, Benedicte Minster7, Ghada Salem3, David Verstraeten2, and Philippe Claeys2 1Laboratoire IDEES UMR 6266 CNRS, University of Rouen Normandy, rue Thomas becket, 76821, Mont-Saint Aignan Cedex, France 2Analytical, Environmental & Geo-Chemistry, Department of Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Elsene, Brussels, Belgium 3ALES, Association Libanaise d'Etudes Speleologiques, Mansourieh El-Matn, Lebanon 4Directorate of Earth and Quaternary, Royal Belgian Institute of Natural Sciences (RBINS), rue Vautier 29, 1000, Brussels, Belgium 5Energie France Pétrole-Nouvelles, 4, avenue de Bois-Préau, 92852, Rueil-Malmaison Cedex, France 6CREEMO, Saint-Joseph University of Beirut, Faculty of Human Sciences, Rue de Damas, BP 17-5208, Beirut, Lebanon 7Laboratoire des Sciences du Climat et de l’Environnement (LSCE/IPSL), UMR 8212 CEA/CNRS/UVSQ, F-91191, Gif sur Yvette Cedex, France Abstract: An important step in paleoclimate reconstructions based on vadose cave carbonate deposits or speleothems is to evaluate the sensitivity of the cave environment and speleothems to regional climate. Accordingly, we studied four caves, located at different altitudes along the western flank of Mount-Lebanon (Eastern Mediterranean). The objectives of this study are to identify the present-day variability in temperature, pCO2, and water isotopic composition and to assess the possible influence of the altitudinal gradient on cave drip waters and cave streams. We present here an overview of the spatial variability of rainwater based on local and regional data, and we compare these data with our results, i.e., temperature, air pCO2, and the isotopic composition of cave water and modern cave calcite collected in 2011 and 2014. The results show that the rainwater isotopic signal is generally preserved in the cave dripwater isotopic composition with some exceptions in large caves with high ceilings where evaporation effects may influence its isotopic composition. The altitude effect observed in rainwater isotopic composition seems to be transferred to the cave dripwater. Different δ18O/100 m gradients between dripwater and rainwater (0.13‰ and 0.21‰, respectively) are noted. This is mainly attributed to the δ18O/100 m value of the dripwater which is site-specific and dependent on i) local processes within the epikarst/soil, ii) the relation to the precipitation altitude gradient and iii) the extension of the defined infiltration basin. Keywords: drip water, isotopic signal, Lebanon, caves, altitude gradient Received 8 February 2019; Revised 26 February 2019; Accepted 26 February 2019 Citation: Nehme C., Verheyden S., Nader F.B., Adjizian-Gerard J., Genty D., De Bondt K., Minster B., Salem G., Verstraeten D. and Claeys P., 2019. Cave dripwater isotopic signals related to the altitudinal gradient of Mount-Lebanon: implication for speleothem studies. International Journal of Speleology, 48 (1), 63-74. Tampa, FL (USA) ISSN 0392-6672 https://doi.org/10.5038/1827-806X.48.1.2253 INTRODUCTION Rainwater and dissolved carbon circulate through the unsaturated zone, i.e. the upper part of the epikarst, Speleothems, which are secondary cave carbonate which is affected by dissolution and is characterized deposits that precipitate from cave drip water are by a mainly vertical transfer of percolation water to increasingly used to reconstruct changes in regional the cave (Hendy, 1971; Bar-Matthews et al., 1996; climate and vegetation. Their isotopic composition, Ford & Williams, 2007; Fairchild & Baker, 2012). δ18O, and δ13C is influenced mainly by respectively the Several cave monitoring programs have been isotope signature of rainwater linked to temperature conducted worldwide, providing information on the (Clarck & Fritz, 1997; Lachniet, 2009) and by the role of local cave environment and hydrology that carbon isotopic composition of dissolved carbon possibly influence stalagmite-based palaeoclimate influenced by the soil bioactivity (δ13C), linked to proxy records (Bar-Matthews et al., 1996; Spotl et al., vegetation and thus to temperature and water 2005; Baldini et al., 2006; Verheyden et al., 2008a; availability (Hellstrom et al., 1998; Genty et al., 2006). Mattey et al., 2010; Miorandi et al., 2010; Tremaine *[email protected] The author’s rights are protected under a Creative Commons Attribution- NonCommercial 4.0 International (CC BY-NC 4.0) license. 64 Nehme et al. et al., 2011; Johnston et al., 2013; Genty et al., 2014; THE STUDY AREA: REGIONAL CLIMATIC Deininger et al., 2014; Van Rampelbergh et al., 2014; CONTEXT AND SITE DESCRIPTION Suric et al., 2016; Beddows et al., 2016). These studies aim at understanding better the registration of the The Levant region in general is mainly influenced nowadays climatic signal in speleothems in order to by the mid-latitude westerlies (Fig. 1A), which more precisely constrain the past climatic records. originate from the Atlantic Ocean, forming a series of In the Levant region, although speleothems subsynoptic low-pressure systems (Gat et al., 2003; from Palestine/Israel are well studied and proxy Ziv et al., 2010) across the Mediterranean Sea. In interpretations well-supported by monitoring winter, cold air plunging south over the relatively programs, the rest of the region is still understudied warm Mediterranean enhance cyclogenesis, creating in terms of speleothem-based paleoclimate studies the Cyprus Low (Alpert et al., 2005). This low- (Nader et al., 2007, Verheyden et al., 2008b, Cheng pressure system drives moist air onshore, generating et al., 2015, Nehme et al., 2015; 2018). Nearly no intense orographic rainfall across the mountains of cave monitoring information is available and only the northern Levant. The duration, intensity, and limited rainwater isotopic data is available (Aouad- track of these storm systems strongly influence Rizk et al., 2005; Gat el al., 2005, Abou Zakhem & the rainfall amount in this region. In summer, the Hafez, 2010). Aouad-Rizk et al. (2005) and Koeniger westerly belt is shifted to the north, following the & Margane (2014) each defined a local meteoric northern shift of the North-African subtropical high water line (LMWL) based on data from central Mount- pressures, and the region experiences hot and dry Lebanon. Both studies display some differences which conditions with more southward winds. In Lebanon will be further discussed in the paper. The Levant (Fig. 1B and 1C), the annual rainfall varies between (East-Mediterranean) is characterized by abrupt 700 and 1000 mm along the coastline and more than temperature and rainfall gradients, due to its current 1400 mm in higher mountains with 4 months snow location on the arid/semi-arid boundary and to its coverage (Shabaan et al., 2015). As a consequence of steep topography between coastal and inland areas. the above circulation system, the climate is seasonal In a first attempt to understand the local with wet winters (November to February) and dry, hot environmental conditions, four Lebanese caves summers (May to October). A general N-S gradient in were investigated for their temperature, pCO2 rainfall amount and mirrored by the isotopic signal concentration, and dripwater isotopic composition. (δ18O and δ2H) is clearly evident from northern Syria Here, modern changes in the rainwater isotopic (Abou Zakhem & Hafez, 2010), to southern Israel/ composition across the steep altitudinal trend of Palestine (Gat et al., 2005). A West-East gradient, Mount-Lebanon, are compiled based on a literature i.e. from the Levantine coastline to inner regions review, and compared with the observed changes in (Fig. 1A), is also visible as a consequence of the modern cave drip waters. The main objectives of this continental and/or altitudinal effects related to the paper are to discuss if rainwater signal is generally Rayleigh distillation processes (Dansgaard, 1964; preserved in the cave dripwaters and to assess the Rozanski et al., 1993). possible influence of the altitudinal gradient on cave Four caves are selected at different altitudes along drip waters and cave streams. This study will help a transect from the coast to the Makmel Mountain, also verify the ability of cave waters in Lebanon to which is the highest peak in the Mount-Lebanon transfer spatial changes in isotopic composition of range (Fig. 2). These are: Kanaan Cave (96 m above rainwaters and by extension of spatial and temporal sea level - asl), Jeita Cave (98 m asl), Mabaage changes in regional climate. Cave (770 m asl), and Qadisha Cave (1720 m asl). Fig. 1. Climate and geographic setting of the study area. A) Eastern Mediterranean map showing the position of the mid latitude winds (http://iridl. ldeo.columbia.edu/Maproom), NS and EW precipitation gradients and δ18O mean values NS and EW precipitation gradients, of rainwater stations over coastal and inner cities (Kailani et al., 2003; El-Asrag, 2004; Aouad-Rizk et al., 2005; Dirican et al., 2005; Gat el al, 2005; Saad et al., 2005; Abou Zakhem & Hafez, 2010; GNIP database); B) Precipitation gradients of Lebanon and histograms of Beirut and the Cedars with mean annual
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